The present invention relates to an image pickup device, and more particularly, to an image pickup device capable of being mounted on a cell phone and a personal computer.
In recent years, highly efficient CPUs, advanced image processing technologies and others have made it possible to handle digital image data easily. In the field of a cell phone and PDA, in particular, a type that is equipped with a display capable of displaying an image has appeared on the market, and rapid progress in radio-communication speed is expected in the near future, which makes us to estimate that transmission of image data will be conducted frequently between these cell phones and PDAs.
Incidentally, under the existing circumstances, these image data are transmitted through internet by a personal computer, after object images have been converted into image data by a digital still camera. In the mode of this kind, however, both a digital still camera and a personal computer need to be provided for transmitting image data. In contrast to this, there is an attempt to mount an image pickup element such as CCD type image sensor on a cell phone. An attempt of this kind makes it unnecessary to have a digital still camera and a personal computer, and it makes it possible for a cell phone that can be carried conveniently to pick up images and to send them to a partner.
However, if a cell phone is made to have functions owned by a digital still camera which is far greater than the cell phone at this stage, the cell phone itself grows greater in size and becomes heavier, resulting in a problem that it cannot be carried conveniently. Further, manufacturing cost for the cell phone is also increased by an amount equivalent to the increase in its size and weight.
In particular, even when a photographing optical system and an image pickup element which are primary constituent factors of the digital camera are unitized, a photoelectrically-converting section of the image pickup element is required to be set appropriately on the focusing position of the photographing optical system, and how to adjust them results in a problem.
For example, when the image pickup element and the photographing optical system are installed on the same base board, it is considered to be difficult to incorporate a photoelectrically-converting section of a photographing element accurately on the focusing position of the photographing optical system, because of factors such as dispersion of a thickness of adhesive agents to be used for the aforesaid installation on the base board and dimensional dispersion of constituent parts. Therefore, for enhancing the focusing position of the photographing optical system and accuracy of incorporating a photoelectrically-converting section of a image pickup element, highly accurate incorporating technology is required, or a mechanism to adjust the focusing position separately is needed, which causes a problem of an increase of manufacture cost. Problems in prior art will be pointed out, referring to the examples.
FIG. 6 is a sectional view showing an example of an image pickup device in the prior art, wherein image pickup element 110 is arranged on base board PC made of glass epoxy resin, and the image pickup element 110 is connected with image processing IC circuit 111 arranged on the reverse side of the base board PC through many wires W coming from a terminal (not shown) on the upper surface of the image pickup element 110.
First housing 101 is arranged to cover the image pickup element 110, and second housing 102 is placed on the first housing 101 so that both of them are fixed together to the base board with bolts 103. Infrared absorption filter 104 is arranged between the first housing 101 and the second housing 102.
An upper portion of the second housing 102 is in a cylindrical form, and lens-barrel 105 housing therein lens 106 is mounted on the second housing 102, through engagement between female screw 102a formed inside the cylindrical upper portion and male screw 105a formed on the lens-barrel 105, to be adjustable in terms of a position in the direction of an optical axis. The lens-barrel 105 is provided with diaphragm portion 105b that is formed on the upper portion of the lens-barrel 105′.
As stated above, the image pickup device in the prior art is a relatively-large device composed of many parts. Therefore, it naturally has a problem of the aforesaid manufacturing cost, and assembling of the parts is time-consuming, while in the course of construction, it is necessary to adjust relative positions between the image pickup element 110 and the lens 106 by rotating the lens-barrel 105. For these problems, TOKKAIHEI No. 9-284617, for example, discloses an image pickup device wherein an image pickup element and an optical system are unitized.
In the image pickup device mentioned above, the number of parts is reduced by the unitization and the device is made to be compact accordingly, which makes it easy to mount the device on a cell phone. Incidentally, the image pickup device of this kind is of a structure wherein four corners of the so-called bare chip representing an image pickup element itself are used for positioning in the direction of an optical axis of a lens and for positioning in the direction perpendicular to the optical axis of the lens, and thereby, a focused image is formed at an appropriate position on a photoelectrically-converting section of the bare chip. However, four corner edges of the bare chip are actually poor in terms of surface accuracy such as flatness and roughness if no action is taken, because each of them is usually a silicone wafer having a thickness of about 0.5 mm which is simply cut. Accordingly, for improving positioning accuracy while using four corner edges of the bare chip, a holding portion for a lens section needs to be extended along each surface to be as long as possible from each of four corners of the bare chip, which causes a problem that the structure is made to be large in size. When wire bonding pads to be connected with a base board are arranged on the surface of the bare chip closer to the lens, in particular, these pads must be avoided, which makes the design of the holding portion to be difficult.
Further, for solving the problems stated above, there is an attempt to construct an image pickup device by providing on a lens a leg portion which is extended to the vicinity of a focal length position of the lens and thereby by making the leg portion to touch an image pickup element directly. The attempt of this kind makes it possible to arrange a photoelectrically-converting section of the image pickup element at the focusing position of the lens, and thereby, to reduce the time to incorporate the image pickup device greatly.
However, in various apparatuses each being equipped with the compact image pickup device of this kind, it is supposed that the image pickup device is vibrated or it is dropped accidentally and is shocked. In these cases, if the leg portion of the lens is in contact with the image pickup element, there is a fear that the lens is loosened by the vibration or the image pickup element is damaged by the shock.
For this problem, it is considered that the lens is brought in pressure contact with the image pickup element while giving a prescribed pressure (see TOKKAIHEI No. 9-284617) by a lens holder and the lens and the image pickup element are fixed by cementing the lens holder to a base board. In this technology, there is a possibility that the lens is loosened when the pressure is reduced by a change with age in thickness of adhesive agents and in forms of parts, although play between the lens and the image pickup element is restrained. Further, there still is a fear the force of the shock makes the lens to damage the image pickup element.